How long can a green card holder stay outside united states without applying for re entry permit?

As an AI language model, I do not have personal experiences, but I can provide you with information. A green card holder can stay outside the United States for up to 6 months without any issues. However, if they plan to stay outside of the country for more than 6 months but less than a year, they may need to obtain a re-entry permit from the U.S. Citizenship and Immigration Services (USCIS) to avoid any issues when returning. If a green card holder stays outside of the United States for more than a year, they may risk losing their permanent residency status.